To compare and test whether a combination of a male hormone (testosterone, given as a daily skin patch made by ALZA Corporation) together with a female hormone (progestagen: levonorgestrel [Norplant II]; two capsules inserted under the skin provided by the Population Council) is more effective than using testosterone alone in suppressing sperm production. The long term goal of the study is to develop a safe, reversible, practical method of contraception for man.